Herpesviruses are distinctive in their ability to establish latency, which is directly associated with cellular transformation and malignancies. Epstein-Barr virus (EBV) and Human herpesvirus-8/Kaposi's sarcoma- associated herpesvirus (HHV-8/KSHV) are associated with several human cancers. In tumor cells, the viruses are in the latent phase and are refractory to currently available antiviral drugs. During the lytic phase or upon reactivation from latency, expressions of all viral genes produce virions and provide targets for antiviral drugs such as Ganciclovir. A viral immediate-early gene, Rta, the replication and transcription activator of KSHV, is necessary and sufficient for disrupting latency and the initiation of KSHV lytic replication, a molecular switch in the KSHV life cycle. Therefore, it is critical to understand the mechanism that controls the expression and activity of Rta. The hypothesis is that multiple cellular signal transduction pathways regulate the balance between latency and lytic replication. It is believed that KSHV reactivation is regulated by both positive and negative cellular signals. We have previously systematically identified the cellular genes that can initiate the reactivation of KSHV. We hypothesize that some cellular genes suppress the reactivation of KSHV from latency. Hence, if we can inhibit the expression of these cellular genes, we may reactivate KSHV from latency. Here, we propose to perform a genome-wide identification of cellular genes that inhibits KSHV reactivation by establishing high-throughput assays to screen a library of siRNAs targeting cellular genes. This study will provide critical and novel information regarding the basic mechanism controlling the initiation of KSHV lytic replication and the development of novel therapies for Kaposi's sarcoma. The concept and approach developed in this project will have general implications and will be directly applicable to EBV- associated malignancies. Herpesviruses maintain latency in tumor cells. We aim to systematically identify cellular signals that regulate the balance between latency and lytic replication via a high-throughput screen. The knowledge will facilitate the development of therapeutic approaches that intentionally reactivate the herpesvirus in tumor cells. [unreadable] [unreadable] [unreadable]